Electrical resistance space heating is one of the most expensive and least efficient ways to heat your whole home; however there are a few applications where they might have their place. When I was in high school I would turn my parent's space heater on high in the winter, put it on the ground, take off my socks, and use it as a foot-warmer. A very energy wasteful foot warmer. Yes, I was too good for socks back then. This was before I became an energy efficiency nerd.
We've already covered some fancy-shmancy electric heaters called Sunheat infrared and Edenpure. Basically, these look fancier than other electric space heaters, but they do the same thing for a lot more money.
The U.S. Dept. of Energy's Energy Efficiency and Renewable Energy (EERE) website has a a great section on Electric Resistance Heating. From the page:
Electric resistance heating converts nearly 100% of the energy in the electricity to heat. However, most electricity is produced from oil, gas, or coal generators that convert only about 30% of the fuel's energy into electricity. Because of electricity generation and transmission losses, electric heat is often more expensive than heat produced in the home or business using combustion appliances, such as natural gas, propane, and oil furnaces.
While space heaters convert almost all of the electricity to heat, that electricity is not that efficient to produce and transport in the first place. Energy used in an electric space heater is obviously electricity and the units of electricity consumption are the kWh. But if you heat with natural gas, propane, or oil, chances are the energy usage is expressed in therms. Because of this difference in units, it can be difficult to compare an electric space heater vs. liquid/gas form of heat. This is why I've written posts on "What is a kWh" and recently, "What is a therm".
The advantage that people who promote electrical space heaters will promote is the fact that you can use zone heating to target only the areas that need to be heated. Unlike central heating that uses a furnace and spread the heat through duct work, most electrical heaters are small and portable. If you only need to heat a small area, like an office or bedroom, and not an entire level, then electrical heaters may make sense. (keep reading for my comparison at the bottom)
The great energy saving blog Energy Boomer has a wonderful article on electric space heaters titled, "How much will it cost to run my electric space heater". The article instructs individuals on how to figure out how much the space heater will cost them to run in their home. Birney Summers (the author of Energy Boomer) touches on whether or not to buy an expensive space heater at the end of his post:
A $250 electric space heater rated for 1,500 Watts and a $20 space heater rated for 1,500 Watts both cost the same on the electric bill and both produce the same amount of heat. One looks like a piece of furniture and the other looks like a space heater. Choose wisely.
EnergyCircle recently posted on electric space heaters with an article titled, "Energy Efficient Space Heaters an Oxymoron? Not So Fast..." The short article ended with an example of where space heaters may work well:
But say you live in a drafty old farmhouse in a cold climate, the kids have gone to college, and you work from home in a study on the first floor. You're working on re-insulating the house and sealing up all the air leaks but haven't gotten there quite yet. And for now you just want to keep warm while you work. You turn down the thermostat, close the doors of your home office and turn on your sleek little electric space heater. Switch on the computer. Have a sip of coffee. Perfect.
Peter Troast, the founder of Energy Circle, chimed in with a comment to give an example of where he uses the electrical space heater:
So I am typing this comment at 64 degrees with the heat provided by the Vornado Vortex....gasp, electric heater. To be sure, it pains me that the Basement Outlet circuit on our eMonitor, because of this 1500 watt device, comprises 46.2% of our electricity use for the last 14 days. And that my heat needs are costing us $2 on a typical day.
Peter's experience inspired me to pull out my natural gas bills so I could compare using natural gas to using an electrical space heater.
We do all of our heating (space, water, food) with natural gas. Now, this may not be a fair comparison because I have a new townhome (better insulated) that faces south (optimal position to get the sunlight), but it will give you an idea of when to consider a space heater, and when to stick with your other form of heat. If anything, it will help walk you through the considerations you should take when comparing different types of heat. It is a thought process you must go through and analyze.
My natural gas bill for January 2010 shows that I used 124.318 therms of natural gas. I pay $0.859 per therm, so the natural gas we used in January cost us $106.79 (this doesn't account for the base fee, taxes, and other miscellaneous charges)! I am not proud of this fact and I share it in hopes that ridicule will inspire us to save even more. But let me break that number down. Since we use natural gas to heat to the levels of our home (3), cook with, and heat our water, I had to make an estimate of how much heat was due solely to the extremely cold weather outside, and how much heat we use to go about our daily lives. I pulled out my natural gas bill from July 2009 to estimate how much natural gas we use to cook with and heat our water. This bill showed that in July we used a paltry 8.184 therms. This is over 15 times less than we used in January! This is why I say it is so important to control your thermostat!
In order to compare how much natural gas we use each day to heat with so we can compare that to an electric space heater, I need to start making some assumptions.
- We heat our ground level for only a few hours each day and only so it isn't freezing when we do laundry (if I had it my way we would never heat this level).
- Our middle floor contains our kitchen, dining area, and living room and we use the second most heat here. We only heat this when we get home from work until we go to bed, and for a short time while making breakfast in the AM.
- We use the most heat upstairs where we sleep and shower. Upstairs we have our bedroom, master bath, guest room, guest bath, and office. We heat this from the time we get home from work until we leave in the morning.
For my assumptions for how much natural gas we use just to heat our living area with I am going to assume we use 50% of our natural gas to heat the upstairs (luckily heat rises so some heat from the middle floor keeps the upstairs warm), 30% to heat the middle floor, and 20% for the basement. Therefore, for the month of January we used about 62 therms to heat our entire upstairs. Divide this by 30 days to get approximately 2 therms per day to heat the entire upstairs. This roughly comes out to be about $1.75 per day to heat our upstairs.
Using these assumptions I can figure out the break-even point of using a electric resistance space heater in our bedroom at night (and not heating our unoccupied guest room/bathroom, office, and master bath) vs. relying on our furnace which uses natural gas and heating space that we don't need to be heating.
The space heater above (and most electrical resistance space heaters) uses 1500 Watts or 1.5 kW. Assuming that I pay $0.10 per kWh I can figure the amount of time I would have to use the space heater each night where it would be cheaper than relying on my natural gas.
Electrical cost to operate space heater = (electrical consumption of heater) x (cost per kWh) x (time heater is on in hrs.)
= 1.5 kW x $0.10 per kWh x ?? hrs
Since I've estimated that it costs me $1.75 per day in natural gas costs to heat my upstairs, I'll use that in the left side of the equation above (the "electrical cost to operate space heater").
$ 1.75 = 1.5 kW x $0.10 per kWh x ?? hrs ==> ?? hrs = 11 hrs and 40 minutes.
In other words, I can run a 1500 Watt electrical resistance space heater for 11 hrs. and 40 minutes at the same cost as our natural gas furnace upstairs. If I use the space heater more than that it is less cost effective. However, there is a chance that the electrical space heater will not put out enough heat to even keep it at a comfortable temperature (we set our thermostat to 70° F at night - yes, I'm aware we should set it lower) and I might need two space heaters, which would definitely defeat the purpose!
If you've actually read this far you know that comparing two forms of heat is not that easy. If you are unnecessarily heating space you dont use (by using central heat) you might be able to benefit from a space heater. But, if you do want to think about using a space heater, know that it can be expensive, and your wife might not like walking into cold rooms all the time!